The California Supreme Court unanimously ruled Thursday that the sponsors of Proposition 8 have the right under state law to appeal a federal court decision that struck down the law.

The case now goes back to the 9th U.S. Circuit Court of Appeals for a future decision on whether the voter-approved ban on same-sex marriage violates the federal Constitution.

Thursday's ruling provides an advisory opinion requested by the federal appeals court earlier this year.

The sponsors of the 2008 ballot initiative are seeking to appeal a decision in which now-retired U.S. District Judge Vaughn Walker struck down the measure, saying that it violates the U.S. Constitution.

But in January, the federal appeals court said that U.S. law as interpreted by the U.S. Supreme Court doesn't appear to allow such an appeal when state officials, including Gov. Jerry Brown and Attorney General Kamala Harris, have refused to defend the measure.

The federal court then asked the state high court to advise whether state law provides such a right.

In Thursday's ruling, the California court said there is such a right and that "the purpose and integrity of the initiative process" set forth in the state Constitution are at stake.

Chief Justice Tani Cantil-Sakauye wrote, "It is essential to the integrity of the initiative process ... that there be someone to assert the state's interest in an initiative's validity on behalf of the public when the public officials who normally assert that interest decline to do so."

Cantil-Sakauye emphasized that the court was not ruling on the validity of Proposition 8 itself, but rather on a procedural matter that affects all initiatives enacted by California voters.